The invention relates to an arrangement for regulating the idling speed of an internal combustion engine by influencing the intake by means of an electromechanical control element which has a valve element which is movable by a solenoid in opposition to the force of a return spring.
Such arrangements are used for regulating the idling speed in order to establish, particularly in automotive vehicles, the lowest possible speed which results in favorable consumption and emission values. If the intake of the internal combustion engine remains constant, variations in the idling speed may occur, in particular, due to different loads which are produced by auxiliary apparatus. In addition to this, at low idling speed the operating condition of an internal combustion engine is close to the unstable speed range in which the engine may die out upon further additional load. For this reason, the flow of air, or intake, upon idling is not set at a fixed value but is regulated according to the variations in the idling speed. For this purpose, the solenoid is acted on by a setting current which is formed, inter alia, as a function of the actual speed of rotation and effects such an adjustment of the valve element, which is connected to the solenoid, that the actual speed of rotation reaches a predetermined desired speed of rotation substantially independently of disturbance variables.
Normally, known arrangements for regulating the idling speed are specifically so developed that when the solenoids are without current the valve element is held in the fully open or fully closed position by the return spring. Only when the solenoid is acted on by the setting current does the valve element move, against the force of the return spring, into a central position located between these two end positions until a balancing of forces prevails between the magnetic force and the force of the return spring.
Upon a failure of the device which produces the setting current or a disturbance in the solenoid, the internal combustion engine is, as a result, operated with the maximum air flow possible within the idling range, which normally results in an undesirably high idling speed, or else with the minimum air flow, with the danger of the engine dying.
The present invention therefore has as its object so further to develop an arrangement for regulating the idling speed of the aforementioned type that, even upon falure of the solenoid or of the current actuating it, a medium idling air flow is established which permits expectation of idling operation which satisfies most cases of load of the internal combustion engine.